Studies have just begun to examine the quantities that affect \(^{16}\) O/\(^{18}\) O in white dwarf merger remnants. The effects on \(^{16}\) O/\(^{18}\) O of the helium burning shell temperature, convective extent of the supergiant envelope and the amount of hydrogen in the shell have been explored [1]}, [2]}. Their values in turn depend on the properties of the merging He-core and CO-core white dwarfs, such as their masses (M\(_{\rm {He}}\)  and M\(_{\rm {CO}}\) ), mass ratios and compositions. The different values of \(^{16}\) O/\(^{18}\) O in dLHdC and RCB stars thus suggest a correlation between the progenitor white dwarfs' properties and dLHdC/RCB formation, which we discuss here. Note however that there are several additional factors that could contribute to the oxygen isotope ratios and remain to be modeled. A big unmodeled source of uncertainty is the effect of the initial composition of the progenitor white dwarfs and post-merger remnant on \(^{16}\) O/\(^{18}\) O. The correlations that we discuss below are based on current understanding and are hence preliminary. Nevertheless, they demonstrate that different properties of merging white dwarfs can result in different values of \(^{16}\) O/\(^{18}\) O, possibly providing a natural explanation for dLHdC versus RCB formation. Additional modeling will help establish robust relations between progenitor properties and dLHdC-RCB stars.
